Microphone for a hearing aid

Abstract

A hearing aid includes a microphone unit arranged in a hearing aid housing. The microphone unit is oriented in the housing relative to a microphone inlet element to cause a pressure equalization that allows acoustic cancellation of vibrations in the microphone unit.

Claims

1. A hearing aid, comprising: a housing having an outer wall enclosing a microphone unit, the outer wall separating the microphone unit from an environment of the hearing aid, the microphone unit comprising a first chamber having a first volume and a second chamber having a second volume; a first inlet opening being arranged at the first or second chamber of the microphone unit; a movable element separating the first chamber and the second chamber; and a microphone inlet element connecting the first inlet opening to a second inlet opening formed in the outer wall of the hearing aid housing, the microphone inlet element being configured to guide sound from the environment via the second inlet opening to the first inlet opening of the microphone unit; where a microphone unit orientation is defined by a first vector perpendicular to the movable element and extending in a direction from the movable element towards the first inlet opening; and where a microphone inlet element orientation is defined by a second vector extending in a direction from the first inlet opening to the second inlet opening; wherein the microphone unit and the microphone inlet element are arranged in the housing so that vibration contributions from the microphone unit to the movable element and vibration contributions from the microphone inlet element are substantially equal but of opposite directions.

2. The hearing aid according to claim 1, wherein the second vector has a component in a direction opposite to the first vector.

3. The hearing aid according to claim 1, wherein the second volume of the second chamber is larger than the first volume of the first chamber.

4. The hearing aid according to claim 1, wherein the microphone unit further comprises a fixed element, arranged in the microphone unit in one of the first or second chamber substantially parallel to the movable element.

5. The hearing aid according to claim 1, wherein the microphone inlet element has a height defined as the distance from the first inlet opening to the second inlet opening.

6. The hearing aid according to claim 5, wherein the height of the microphone inlet element fulfills $h=\frac{p_{\mathrm{inlet}}}{\left(\mathrm{rho}*a_z\right)},$ where p.sub.inlet is the pressure build-up in the inlet element, rho is the density of air and a.sub.z is an environmental acceleration acting on the housing.

7. The hearing aid according to claim 5, wherein the height of the inlet element is dimensioned such that the contribution from the microphone inlet element to the vibration sensitivity of the microphone is equal to, but of opposite sign to the contribution from the microphone unit.

8. The hearing aid according to claim 4, wherein the movable element and the fixed element forms a capacitor within the microphone unit.

9. The hearing aid according to claim 4, wherein an air gap is defined between the fixed element and the movable element, so that a pressure difference across the movable element forces the movable element to move towards and away from the fixed element.

10. The hearing aid according to claim 4, wherein the movable element is a diaphragm and the fixed element is a back plate, the back plate holding a static charge so that a voltage is created across the back plate when a pressure difference arises across the diaphragm.

11. A method for designing a hearing aid optimized for vibration cancellation, comprising the steps of: i) providing a housing having an outer wall, ii) enclosing a microphone unit in said housing, the outer wall separating the microphone unit from an environment of the hearing aid, and the microphone unit comprising a first chamber having a first volume; a second chamber having a second volume; a first inlet opening being arranged in the first or second chamber; a movable element arranged to separate the first chamber and the second chamber; iii) connecting a microphone inlet element to the first inlet opening and to the outer wall of the housing at a second inlet opening, wherein the microphone inlet element is configured to guide sound from the environment of the hearing aid to the microphone unit; where a microphone unit orientation is defined by a first vector perpendicular to the movable element and extending in a direction from the movable element to the first inlet opening; and a microphone inlet element orientation is defined by a second vector extending in a direction from the first inlet opening to the second inlet opening; iv) arranging the microphone unit and the microphone inlet element in the housing so that the microphone unit and the microphone inlet element, are arranged in the housing so that vibration contributions from the microphone unit to the movable element and vibration contributions from the microphone inlet element are substantially equal but of opposite directions.

12. The method according to claim 11, wherein step iv further comprises arranging the microphone unit and the microphone inlet element in the housing so that the second vector has a component in a direction opposite to the first vector.

13. The method according to claim 11, wherein the inlet element has a height, defined as the distance from the first inlet opening to the second inlet opening, the height fulfilling: $h=\frac{p_{\mathrm{inlet}}}{\left(\mathrm{rho}*a_z\right)},$ where p.sub.inlet is the pressure build-up in the inlet element, rho is the density of air and a.sub.z is an environmental acceleration acting on the housing.

14. The method according to claim 11, wherein the microphone unit further comprises a fixed element, arranged in the microphone unit in one of the first or second chamber substantially parallel to the movable element.

15. The method according to claim 14, the movable element and the fixed element forms a capacitor within the microphone unit.

16. The method according to claim 14, wherein an air gap is defined between the fixed element and the movable element, so that a pressure difference across the movable element forces the movable element to move towards and away from the fixed element.

17. The method according to claim 14, the movable element is a diaphragm and the fixed element is a back plate, the back plate holding a static charge so that a voltage is created across the back plate when a pressure difference arises across the diaphragm.

18. The method according to claim 11, wherein the microphone inlet element has a height defined as the distance from the first inlet opening to the second inlet opening.

19. The method according to claim 18, wherein the height of the inlet element is dimensioned such that the contribution from the microphone inlet element to the vibration sensitivity of the microphone is equal to, but of opposite sign to the contribution from the microphone unit.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The aspects of the disclosure may be best understood from the following detailed description taken in conjunction with the accompanying figures. The figures are schematic and simplified for clarity, and they just show details to improve the understanding of the claims, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts. The individual features of each aspect may each be combined with any or all features of the other aspects. These and other aspects, features and/or technical effect will be apparent from and elucidated with reference to the illustrations described hereinafter in which:

(2) FIG. 1 illustrates schematically a pressure build-up in a microphone unit influenced by an acceleration;

(3) FIG. 2 illustrates schematically the membrane inertia of a microphone unit influenced by acceleration;

(4) FIG. 3 illustrates the combined pressure build-up in a microphone unit influenced by an acceleration;

(5) FIG. 4 illustrates a microphone unit and inlet element orientation according to an embodiment of the disclosure, where the housing is influenced by an acceleration at a first point in time;

(6) FIG. 5 illustrates the microphone unit and inlet element orientation according to the embodiment of FIG. 4 at a second point in time and under influence by an acceleration;

(7) FIG. 6 illustrates another arrangement of a microphone unit and an inlet element in a hearing aid housing according to an embodiment of the disclosure;

(8) FIG. 7 illustrates an orientation of a microphone unit and an inlet element, according to another embodiment of the disclosure, where the inlet element is arranged in a second chamber having a larger volume than a smaller first chamber;

(9) FIG. 8 illustrates another orientation of an inlet element and a microphone unit according to the disclosure; and

(10) FIG. 9 illustrates a further possible arrangement of an inlet element and a microphone unit according to embodiments of the disclosure.

DETAILED DESCRIPTION

(11) The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts according to the disclosure may be practiced without these specific details. Several embodiments of the device and methods are described by various functional units, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as elements). Depending upon particular application, design constraints or other reasons, these elements may be implemented using electronic hardware, computer program, or any combination thereof.

(12) The electronic hardware may include microprocessors, microcontrollers, digital signal processors (DSPs), discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. Computer program shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

(13) An electronic device according to the disclosure preferably includes a hearing aid that is adapted to improve or augment the hearing capability of a user by receiving an acoustic signal from a user's surroundings, generating a corresponding audio signal, possibly modifying the audio signal and providing the possibly modified audio signal as an audible signal to at least one of the user's ears. The electronic device may further refer to a device such as an earphone or a headset adapted to receive an audio signal electronically, possibly modifying the audio signal and providing the possibly modified audio signals as an audible signal to at least one of the user's ears. Such audible signals may be provided in the form of an acoustic signal radiated into the user's outer ear, or an acoustic signal transferred as mechanical vibrations to the user's inner ears through bone structure of the user's head and/or through parts of middle ear of the user or electric signals transferred directly or indirectly to cochlear nerve and/or to auditory cortex of the user.

(14) An electronic device, such as a hearing aid according to the disclosure includes i) an input unit such as a microphone unit for receiving an acoustic signal from a user's surroundings and providing a corresponding input audio signal, and/or ii) a receiving unit, such as a receiver, loudspeaker or speaker, for electronically receiving an input audio signal. The hearing aid further includes a signal processing unit for processing the input audio signal and an output unit for providing an audible signal to the user in dependence on the processed audio signal.

(15) The input unit may include multiple input microphones, e.g. for providing direction-dependent audio signal processing. Such directional microphone system is adapted to enhance a target acoustic source among a multitude of acoustic sources in the user's environment. In one aspect, the directional system is adapted to detect (such as adaptively detect) from which direction a particular part of the microphone signal originates. This may be achieved by using conventionally known methods.

(16) The signal processing unit may include amplifier that is adapted to apply a frequency dependent gain to the input audio signal. The signal processing unit may further be adapted to provide other relevant functionality such as compression, noise reduction, etc. The output unit may include an output transducer such as a loudspeaker/receiver for providing an air-borne acoustic signal transcutaneously or percutaneously to the skull bone or a vibrator for providing a structure-borne or liquid-borne acoustic signal.

(17) In order to get a better understanding of the importance of extinguishing the sound pressure level (SPL) arising from microphone imperfections, the vibration sensitivity of a microphone will briefly be touched upon in the following with reference to FIGS. 1 to 3.

(18) In general, hearing aid microphone units 10 have the same basic functionality. A charged back plate (i.e. a fixed element) 11 and a dynamic membrane 12 (e.g. a diaphragm, also denoted a movable element) forms a capacitor. When sound enters through the first inlet opening 13 of the microphone unit 10, the pressure from the sound wave forces the membrane 12 to move. The movement of the membrane causes a change in the voltage across the capacitor. Thus, any change in pressure in the volume where the membrane 12 is suspended in a microphone unit 10 causes the membrane 12 to move, why a pressure caused by other sources than a sound pressure level (SPL) from the surrounding environment of the hearing aid when and detected by the microphone unit may create unwanted change in voltage across the capacitor. Various sources causing an unwanted change in output could arise from a vibration acting on the microphone, the vibrations influencing the microphone unit from substantially all directions.

(19) A source causing unwanted output signals of the microphone unit 10, is coming from the inertia of the membrane 12, as illustrated in FIG. 2. When the microphone unit 10 moves, for example due to vibrations, the back plate 11 follows, since the back plate 11 is structurally connected to the housing of the microphone unit 10. The membrane 12 does not follow immediately, since the membrane is suspended and the mass of the membrane 12 (i.e a diaphragm) has to be accelerated by a force before it moves. The movement of the membrane 12, due to the force created from the membrane inertia, illustrated in FIG. 2 as arrow 15, is only active when the microphone is vibrated in the direction, in which the membrane 12 can move. The direction of vibration, in which the diaphragm can move is a direction of vibration coming perpendicular to the orientation of the diaphragm, illustrated as the z-direction defined by arrow 14 in FIGS. 1 to 3. The vibration will act on the membrane 12 and potentially cause the membrane 12 to move in the direction shown by arrow 15, resulting in an unwanted charge to the back plate 11 that is not related to a sound pressure level (SPL) caused by the environmental sound and detected by the microphone unit itself. The likely inconsistent and out of phase movement of the membrane 12 and the back plate 11 due to vibrations changes the distance between membrane and back plate, and an output signal is present, even though a sound pressure level (SPL) is not.

(20) Another source to unwanted outputs of the microphone arises due to encapsulated (inerted) air inside the microphone unit 12, illustrated in FIG. 1. When the microphone unit 12 is accelerated in the direction defined by arrow 14, air trapped inside the microphone unit 12 will not move unless being pushed by the microphone unit walls 10a, 10b, 10c, 10d (or other internal parts). Since this is not symmetric a pressure will build up. The force created due to pressure differences arising from the vibration inside the microphone will act on the membrane 12 in dependence on the pressure-build across the membrane 12.

(21) As an example, illustrated in FIG. 1, a vibration applied to the microphone unit 10 in a direction corresponding to arrow 14, influences air trapped inside first 16 and second 17 chamber. The first chamber 16 has a first volume, the first volume being different than a second volume of the second chamber 17. The two chambers are separated by the movable element 12, also denoted a membrane or diaphragm. The pressure build-up on each sides of the membrane 12 is as shown in FIG. 1 denoted P+, for a substantially positive pressure, and P for a substantially negative pressure. As seen in FIG. 1, the pressure build-up on each side of the membrane creates a slightly more positive pressure on the side of the membrane facing the first chamber 16, and in relation thereto a slightly lower pressure on the side of the membrane facing the second chamber 17. Therefore, a resulting force created from the pressure difference inside the microphone unit 10 during acceleration thereof, will force the membrane 12 in a direction according to arrow 18 illustrated in FIG. 1. In addition to the pressure build-up inside the microphone unit as illustrated in FIG. 1, a contribution from a pressure build-up in the y-direction will also exist. Thus, a pressure build-up in the substantially longitudinal direction of the microphone from side wall 10d to 10c is also present and should be accounted for.

(22) The vibrational behaviors of the back plate 11 and the membrane 12 together with vibration of encapsulated air influences the vibration sensitivity of the microphone unit and the combined force, illustrated by arrow 19 in FIG. 3, acting on the membrane during vibrations. The vibrational direction being defined according to arrow 14 results in the membrane moving towards and away from a fixed element, also denoted the back plate 11 of the microphone unit 10. This membrane movement due to vibrations results in a capacitive effect across the electrically charged back plate and essentially an output sound pressure level (SPL) of the microphone unit. The resulting SPL, arising from vibrations influencing the microphone unit are generally identified as the microphones sensitivity towards vibrations. Suppliers of microphone units therefore often provides information on the microphone sensitivity value, such that the correct microphone for a needed implementation can be chosen by a user. Microphones may be build such as to optimize the microphone sensitivity to a specific purpose, and the build-in vibration sensitivity is evaluated, when a microphone is chosen for a specific use.

(23) From considerations, utilizing the in-build microphone vibration sensitivity, realization of the possibility of extinguishing the SPL output of the microphone caused by vibrations of the microphone unit is present. The substantially sufficient extinguishing of unwanted SPL output being obtained by providing a suitable orientation of the microphone unit in relation to an inlet element, where the inlet element extends from a first inlet opening in the microphone unit to a second inlet opening at a wall of a hearing aid housing. The inlet element should be understood to be any type of element, which are able to guide sound from an opening in the hearing aid housing to an opening in the microphone unit. The inlet element could therefore also be termed an inlet guide or sound inlet guide etc.

(24) Different configurations of the microphone unit and the inlet element in relation to each other are illustrated in FIGS. 4 to 9 and will in the following be touched upon for providing a better understanding of the present disclosure.

(25) Referring initially to FIGS. 4 and 5 parts of a hearing aid 1 is illustrated. The hearing aid 1 comprises a housing having an outer wall 100 enclosing a microphone unit 110. The outer wall 100 of the housing separates the microphone unit 110 from an environment. Furthermore, the microphone unit 110 comprises walls 110a, 110b, 110c, 110d, which separates the microphone unit from other electronic devices within the hearing aid.

(26) As illustrated in FIGS. 4 and 5, the microphone unit 110 comprises a first chamber 116 having a first volume and a second chamber 117 having a second volume. The first chamber 116 comprises a first height h1 and the second chamber 117 comprising a second height h2. In general, the first and second chamber 116, 117 defines a first and a second volume, which preferably are different.

(27) In addition, a first inlet opening 113 is arranged in the first chamber 116 and a membrane 112 (such as a diaphragm, which is construed as a movable element) is arranged in the microphone unit 110. The diaphragm separates the first 116 and second chamber 117.

(28) Furthermore, a fixed element 111 (such as a charged back plate) is arranged in the microphone unit and provides an electrical charge. Thus, the charged back plate and the diaphragm provides for a capacitive effect of the microphone unit 110 allowing for incoming sound to be processed into an electrical signal, which are further processed by suitable elements, such as circuits, amplifier and speakers (not shown) to account for a hearing loos.

(29) A microphone inlet element 120 is connected to the first chamber 116 at the first inlet opening 113 and to the outer wall 100 of the housing at a second inlet opening 121. In this way, the microphone inlet element is configured to guide sound from the environment (i.e sound delivered to the surface of the hearing aid housing) to the microphone unit 110.

(30) The orientation of the microphone inlet element 120 in relation to the microphone unit 110 is in more detail defined by a microphone unit orientation 122 and an inlet element orientation 123. The microphone unit orientation is defined by a first vector 122, which first vector extends perpendicular to the membrane 112 in a direction from the membrane 112 towards the first inlet opening 113. The inlet element orientation on the other hand is defined by a second vector 123 extending in a direction from the first inlet opening 113 to the second inlet opening 121. As illustrated in the FIGS. 4 and 5 the microphone unit 110 and the inlet element 120, is from this vector direction definition arranged in the housing so that the second vector 123 has at least one component 124 in a direction opposite to the first vector 122.

(31) When the hearing aid housing and accordingly the microphone unit 110 is influenced by a vibration in the direction indicated by arrow 14, the pressure building up inside the microphone unit 110 and the inlet element 120 is in a first static moment in time as illustrated in FIG. 4. As seen in FIG. 4, a positive pressure builds up in the first chamber 116 of the microphone unit 110 and in relation to the pressure in the first chamber, a slightly more negative pressure builds up on the side of the membrane 112 facing the second volume 117. In addition, the inlet element 120 has a pressure build up, which in the static moment in time illustrated in FIG. 4 results in a substantially negative pressure at the end of the inlet element 120, which connects to the first inlet opening 113 of the microphone unit 110. Thus, the resulting pressures build-up at each side of the first inlet opening 113 is of opposite signs, and therefore counteracts each other during vibration of the hearing aid housing. In accordance herewith a pressure, p.sub.surface also builds up on the outer walls (i.e. walls facing the environment where sound enters the hearing aid) of the housing. The surface pressure should therefore also be taken into consideration when estimating the pressure building up in the inlet element, as will become apparent in the following.

(32) Depending on the size of the two pressures building up inside the microphone (i.e. the microphone vibration sensitivity explained according to FIGS. 1 to 3) and the pressure building up in the inlet during vibrations, the movement of the membrane 112 caused by the vibrations according to arrow 14, will be substantially counteracted by the pressure building up in the inlet element 120 during vibrations when the inlet element 120 and the microphone unit 110 are arranged in relation to each other as just described.

(33) In a second static moment of time, where the vibration direction defined by arrow 114a, is opposite to the one defined in FIG. 4, the microphone unit 110 and the inlet element 120 arranged in accordance with FIG. 4 undergoes a similar pressure build-up. In this case the pressure build-up on each side of the membrane 112 is equal to the one defined in FIG. 4 but of opposite signs, and the pressure build-up in the inlet element is equally of similar pressure, but with opposite sign. Thus, the resulting influence on the membrane is similarly that the positive pressure building up at the first inlet opening 113 in the inlet element 120 counteracts the pressure building up the membrane 112, forcing the membrane to stay in place.

(34) Thus, with a microphone unit and inlet element arranged in relation to each other in the hearing aid according to the configuration just described and in accordance with the following embodiments, it is possible to substantially cancel out the in-build microphone vibration sensitivity of the microphone unit, whereby unwanted sound pressure levels are prevented in the hearing aid.

(35) Accordingly, the microphone unit 110 and the microphone inlet element 120 are arranged relative to each other so that contributions from the microphone unit 110 and the microphone inlet element 120, respectively, to a vibration sensitivity of the microphone when located in the hearing aid, are substantially equal but of opposite sign. Accordingly, the hearing aid construction with a specific inlet element orientation and microphone unit orientation according to the disclosure provides a vibration cancellation which does not require any signal processing, but is merely acoustic in the form of a pressure equalization.

(36) With reference to the concept of arranging the microphone unit 110 and the inlet element 120 in the previously described manner, it is noted that the microphone inlet element 120 in an embodiment, is dimensioned with a height h3, illustrated in FIGS. 4 and 5. The height h3 of the inlet element 120 is defined as a distance from the first inlet opening 113 to the second inlet opening 121. The height is measured along the longitudinal length of the inlet element 120 in a direction parallel with the wall 110b of the microphone unit 110.

(37) For providing an optimal counteraction of the pressure building up inside the microphone unit 110 during vibrations, the height h3 of the inlet element 120 is designed by using the following equation;

(38) $h=\frac{p_{\mathrm{inlet}}}{\left(\mathrm{rho}*a_z\right)},$
where p.sub.inlet is the pressure build-up in the inlet element, rho is the density of air and a.sub.z is an environmental acceleration acting on the housing.

(39) In addition to this calculation, an estimation of the surface pressure p.sub.surface, on the outer sides exposed to the environment and incoming sound could preferably also be taken into account for achieving an optimal cancellation. Therefore, the surface pressure, should be added to p.sub.inlet, thus p.sub.inlet=P.sup.++P.sub.surface, where P.sup.+ is the pressure of the inlet element at the first inlet opening 113, as illustrated in for example FIG. 6. The + simply defines whether the pressure at the side of the first inlet element 113 is of negative or positive value, upon influence from a vibration acting on the housing.

(40) Thus, in order to cancel out the vibration sensitivity of the microphone efficiently, the pressure build-up in the inlet element 120 should be of equal size but opposite sign to the pressure build-up in the microphone unit during vibrations. The height of the inlet element may therefore be designed such that the pressure build-up in the inlet is equal to the vibration sensitivity of the microphone unit.

(41) The pressure build-up in the microphone unit 110 can be calculated from the in-build microphone sensitivity value given in dB SPL/g. When knowing the microphone sensitivity value, the pressure in the microphone unit, which the pressure build-up in the inlet element should counteract is calculated, as given in the following example.

(42) If a microphone unit has a given vibration sensitivity on 60 dB SPL/g, this corresponds to a sound pressure of 0.02 Pa/g. Thus the inlet element should be designed such that the pressure, p.sub.inlet, build up in the inlet element is 0.02 Pa/g. Using the equation, this result in an optimal inlet height of

(43) $h=\frac{0.02\mathrm{Pa}\text{/}g}{\left(1.204\mathrm{kg}\text{/}{m}^3*\frac{9.81m}{s^2}\right)}=1.7\mathrm{mm}$

(44) Thus, for a microphone unit having a vibration sensitivity of 60 dB SPL/g, the inlet height should preferably be 1.7 mm and the inlet element should be arranged in relation to the microphone unit in accordance with the previous description thereof.

(45) In this way, the height of the inlet element is dimensioned such that the contribution from the microphone inlet element, relative to the vibration sensitivity of the microphone unit is of equal size but of opposite sign to the contribution from the microphone unit.

(46) Referring now to FIG. 6 in further details, an embodiment according to the disclosure is shown. In general, the microphone unit 110 and the microphone inlet element 120 is arranged and orientated in relation to each other in a manner as previously described. In more detail, the embodiment illustrated in FIG. 6 generally constitutes the same elements and components, i.e. the microphone has a first volume 116 and a second volume 117 and a movable membrane 112 separating the two volumes. Furthermore, the microphone inlet element 120 is in one end connected to the first inlet opening 113 arranged in the microphone unit 110 in the first volume and a second inlet opening 121 connected to a wall 100 of the hearing aid housing. In comparison with FIGS. 4 and 5, the microphone unit 110 and inlet element 120 has been turned 180 degrees in FIG. 6. The embodiments shown in FIGS. 4 to 6 therefore illustrates orientations of the inlet element and the microphone in relation to each other and where the inlet element has been arranged in connection with a first inlet opening provided in the first volume, and which fulfills the requirement of substantially cancelling out the vibration sensitivity according to the disclosure.

(47) As seen from FIG. 6, the microphone unit 110 and microphone inlet element 120 is arranged such that a microphone unit 110 orientation vector 122 extends in an opposite direction to a vector component 124 of an inlet element orientation vector 123 (i.e. the second vector), and this arrangement therefore fulfill the requirements for obtaining a microphone vibration sensitivity cancellation. Accordingly, the optimal inlet height may be calculated as previously described.

(48) Referring now to FIG. 7 an embodiment according to the disclosure, where the inlet element 120 is arranged in the second volume, is illustrated. In accordance with the previously described Figures, the first vector 122 extending from the movable membrane 112 towards the first inlet opening 113 is extending in an opposite direction to a vector component 124 defined by the second vector 123, where the second vector indicates the orientation of the inlet element 120. This arrangement will in a similar manner as previously described be able to cancel out the vibration sensitivity of the microphone. The main differences between FIGS. 4 to 6 and 7, is therefore only to illustrate that the inlet element 120 may be provided in both chambers 16, 17 of the microphone unit 110, where at least one of the chambers comprises a volume that is bigger than the other chamber.

(49) Accordingly, and as illustrated in the Figures, the first and second volumes of the microphone unit may be configured such that the second volume of the second chamber is larger than the first volume of the first chamber. However, the volumes could be of the same size.

(50) In general, the first volume, wherein the microphone inlet opening 113 is arranged is defined as a front volume and the larger second volume as a back volume.

(51) As illustrated in the embodiments according to the Figures, the microphone unit further comprises a fixed element 112 (i.e. a back plate), arranged in the microphone unit in one of the first or second chamber substantially parallel to the movable element 111 (i.e. the membrane).

(52) Accordingly, the movable element and the fixed element forms a capacitor within the microphone unit. The capacitive effect of the fixed plate and the membrane creates a voltage inside the microphone unit which is transformed into a signal provided to a receiver which transmit an audible sound signal to the ear drum of the hearing aid user.

(53) The capacitive effect of the fixed plate and the membrane arises due to the movable properties of the membrane and an air gap provided between the fixed element and the movable element, so that a pressure difference across the movable element forces the movable element to move towards and away from the fixed element. When sound waves hits the movable element (i.e. the membrane, also denoted diaphragm), the pressure difference across the membrane forces the membrane to move towards and away from the fixed element whereby a voltage is created.

(54) Accordingly, the movable element is a diaphragm and the fixed element is a back plate, where the back plate in case of an electret-type microphone may hold a static charge so that a voltage is created across the back plate when a pressure difference arises across the diaphragm.

(55) Referring now to FIG. 8, an embodiment according to the disclosure is illustrated, wherein the microphone unit comprises a first inlet opening 113 in a bottom wall part 110b of the microphone unit. Such microphone could for example be of the MEMS type microphone, but should not exclude a similar arrangement with an electret type microphone. The relevance as such does not lie within the microphone type but rather the arrangement of the microphone unit within the housing and in relation to the inlet element.

(56) In the embodiment shown, the microphone unit 110 orientation is defined by the first vector extending in a direction from a movable element 112 towards the first inlet opening 113. In addition, the microphone inlet element 120 extends from the first inlet opening 113 towards a second inlet opening 121 in an outer wall 100 of the hearing aid housing so that a second vector 123 defines the orientation of the inlet element. Thus, in accordance with the previous described figures, the microphone unit 110 and the inlet element 120 are arranged in relation to each other so that the a vector component 124 of the second vector 123 extends in an opposite direction to the first vector 122. This arrangement therefore also fulfills the arrangement requirements for cancelling out the microphone sensitivity.

(57) In the embodiment shown in FIG. 8, the microphone unit 110 is arranged in connection with two microphone inlet elements 120a, 120b. The microphone inlet opening 113 substantially receives sound from both inlet elements 120a, 120b. The microphone inlet elements 120a, 120b could be two separate elements or implemented as one element into which the inlet opening 113 looks.

(58) In a further embodiment illustrated in FIG. 9, a microphone unit 110 is arranged in a hearing aid housing 1, the microphone unit 110 could for example be of a MEMS-type. In this embodiment, the first inlet opening 113 of the microphone unit 110 looks into an inlet element comprising a first end 120a and a second end 120b. In each end 120a, 120b, a second inlet opening 120 is provided for guiding environmental sounds into the microphone inlet opening 113. In a similar manner as described in relation to the previous embodiments, the inlet element 120a, 120b comprises a height h3, which may be designed in accordance with the previously described method to efficiently cancel out the microphone vibration sensitivity.

(59) Further, illustrated in FIG. 9 is the arrangement of the microphone unit 110 in relation to the inlet element 120a, 120b to provide a substantially sufficient microphone vibration cancellation. In a similar manner as previously described the microphone unit orientation is defined by a first vector 122 extending in a direction from a movable element 112 towards the first inlet opening 113. The microphone inlet element 120a. 120b extends from the first inlet opening 113 towards a second inlet opening 121 in an outer wall of the hearing aid housing 1 so that a second vector 123 defines the orientation of the inlet element (illustrated in relation to inlet element part 120a). Thus, in accordance with the previous described figures, the microphone unit 110 and the inlet element 120a, 120b are arranged in relation to each other so that the a vector component 124 of the second vector 123 extends in an opposite direction to the first vector 122. This arrangement therefore also fulfills the arrangement requirements for cancelling out the microphone sensitivity.

(60) It is intended that the structural features of the devices described above, either in the detailed description and/or in the claims, may be combined with steps of the method, when appropriately substituted.

(61) As used, the singular forms a, an, and the are intended to include the plural forms as well (i.e. to have the meaning at least one), unless expressly stated otherwise. It will be further understood that the terms includes, comprises, including, and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will also be understood that when an element is referred to as being connected or coupled to another element, it can be directly connected or coupled to the other element but an intervening elements may also be present, unless expressly stated otherwise. Furthermore, connected or coupled as used herein may include wirelessly connected or coupled. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items. The steps of any disclosed method is not limited to the exact order stated herein, unless expressly stated otherwise.

(62) It should be appreciated that reference throughout this specification to one embodiment or an embodiment or an aspect or features included as may means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the disclosure. The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects.

(63) The claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean one and only one unless specifically so stated, but rather one or more. Unless specifically stated otherwise, the term some refers to one or more.

(64) Accordingly, the scope should be judged in terms of the claims that follow.